Hydrocarbons are among the most versatile substances available to mankind, being suitable for conversion into various types of fuels, plastics, dyestuffs, lubricating oils, explosives, medicinals, and other products. The hydrocarbons which form the basis for such products are to be found in nature in a variety of forms including natural gas, oil, coal, and related materials. Certain hydrocarbons are also available as a result of manufacturing processes, for example, those derived from the waste products of refining operations, and other manufacturing processes.
Unfortunately, the molecular form in which such hydrocarbons are available is not always suitable for the uses to which they are to be put, frequently making it necessary to alter their chemical structure.
In the past, a variety of ways have been resorted to in order to accomplish such molecular restructuring. For example, resort has been had to chemical "rearrangements", usually accomplished with the assistance of a catalyst to form new compounds having the same molecular weight, but displaying different properties.
The Fischer-Tropsch process is another way in which restructuring can be carried out. The method includes the synthesis of water gas, accomplished by passing steam over hot coke, followed by its enrichment with hydrogen, and the subsequent reaction of the gas in the presence of a catalyst to provide hydrocarbons ranging from C.sub.3 to C.sub.35, and even higher. A variety of catalysts and operating conditions have been employed for the reaction.
Lignite, coal, various tars, and related materials have also been catalytically hydrogenated to produce fuel oils. In addition, natural gas has been reacted with steam to produce carbon monoxide and hydrogen, such reaction products having then been converted to methyl alcohol by the use of aluminum, copper, and zinc based catalysts. The alcohol has subsequently been employed to make olefins, the latter forming the starting materials for the manufacture of middle distillates.
Acetylene can also be prepared by partially oxidizing natural gas in the presence of oxygen. Furthermore, the cracking of natural gas rich in ethane, propane, or butane at high temperatures, for example, yields a high proportion of ethylene, among other products. In like manner, the thermocracking of aromatic compounds such as naphtha results in the production of higher olefins.
In addition to the preceding, a variety of other reforming systems have been developed, for instance, involving the dehydrogenation of cyclohexanes to form aromatic hydrocarbons, the dehydrocylization of certain paraffins to yield aromatics, and the isomerization of straight-chain to branched-chain molecules. Some of these systems simply rely on heat and pressure for the transformation, while others are accomplished catalytically. Hydrogen is also used in hydroforming operations in the presence of heat, pressure, and catalysts to convert olefinic hydrocarbons to branched-chain paraffins.
While all of the preceding accomplish molecular restructuring of the starting materials, many of the processes suffer from excessive operating costs. Still others require extensive investment in expensive processing equipment. Consequently, many of the processes have been of value chiefly in special circumstances such as during wartime, or in other unusual situations.